Method of making a fuse by securing the terminals by magnetic forming



ug- 1, 1967 F. l.. CAMERON r-:TAL 3,333,336

METHOD OF MAKING A FUSE BY SECURING THE TERMINALS BY MAGN lC FORMING Filed C 15, 1965 'I FIG. 2. '5

ATTORNEY United States Patent O 3,333,336 METHOD F MAKING A FUSE BY SECURING THE TERMINALS BY MAGNETIC FORMING Frank L. Cameron, North Huntington Township, Irwin,

and Wilson C. Good, Levelgreen, Trafford, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 13, 1965, Ser. No. 495,490 3 Claims. (Cl. 29-623) This invention relates to improvements in fuses, and more particularly to an improved fuse in which the fuse ferrule or end cap makes firm electrical connection with the fusible element fand is very strongly atiixed to the fuse tube, and the fuse is thus able to withstand pressures generated 'Within the fuse resulting from the dissipation of inductive energy stored in the circuit at the time of interruption.

Our invention also relates to a new and improved method of constructing such a fuse.

Current limiting fuses are frequently called on to eiectively clear large fault current short-circuits at high voltage. This fault clearing must be accomplished without display or discharge from the fuse. By nature of its construction, this type of fuse actually forces a current zero and interrupts at other than the natural current zero of the circuit. As a result of this, the inductive energy stored in the circuit at the time of interruption must be dissipated within the lfuse itself. Consequently, significant pressures are generated within the fuse :and must be contained by the fuse. It is thus imperative that the fuse ferrules or end caps be strongly lafiixed to the fuse tube.

[Prior art methods of securing a ferrule to a fuse tube include pinning, cementing and rolling, actually forcing the ferrule metal into premachined grooves cut in the tubing, etc. Each of these methods has some inherent disadvantages. For example, pinning and rolling require a significant wall thickness of the fuse tube in order to compensate for the actual weakening of the tube when it is drilled for pinning, or grooved for rolling. A minimum Wall thickness tube can be and is used when an epoxy cement is employed to fasten the ferrule. The basic disadvantages here, however, are the necessity for a proper tube preparation for the cementing operation, the long baking and set times, and the problems of handling. Furthermore, under some specifications a completely nonmechanical, cemented connection is not acceptable.

In summary, our fuse includes a fusible element disposed within a fuse tube, the fusible element being either helical or inthe form of a wire extending through the fuse tube, the fusible element having strips of conductive material, for example copper, secured to both ends thereof. In

one method of preparing our fuse, the ends of the Ifuse tube, composed for example of glass melamine, are coated with a brush coat of sodium silicate (water glass); this surface is then dusted with a quantity of silicon carbide grit, for example, of grain size No. 150, to increase the holding force between ferrule and tube. The ends of the copper strips yare bent around the ends of the fuse tube and are further bent back over the coating, and the copper strip may be [further bent to extend substantially longitudinally along the axis of the opening through the fuse tube. The ferrule is then slipped over the end of the fuse tube and coating, and is then secured to the fuse tube by a process known las magnetic forming, sometimes called magneforming This includes inserting the ferrule with the fuse tube loosely joined in a rigid coil through which a high current is caused to flow as a result of a discharge of capacitors, a Iforce being set up in the ferrule which tends to compress the ferrule and which effectively binds the ferrule to the fuse tube and seals it.

3,333,336 Patented Aug. l, 1967 rice In another embodiment of our invention We'employ ceramic fuse tubes, the ends 4of which are wrapped with a single band of pressure sensitive adhesive tape before the magnetic forming operation takes place, such as a tape composed of cellulose acetate with an adhesive, or polyester. This tape gives some impact resistance and enables the magnetic crimping force to be set very liigh, resulting in an effective and strong seal between ferrule and fuse tube, yet without any impact damage to the ceramic tu-be. In this instance, the magneforming operation is used to make the electrical connection as well as to seal the ferrule and the fuse tube. Y

Accordingly, a primary object of the invention is to provide a new and improved fuse.

Another object is to provide a new and improved method of constructing a fuse.

A further object is to provide anew and improved fuse characterized by a sufficiently strong bond between ferrule and fuse tube so the pressures generated within the fuse tube by the interruption of a circuit with an accompanying dissipation lof energy will not damage the fuse.

A further object is to provide a new and improved method of constructing a fuse having a very strong bond between fuse tube and ferrule.

These and other objects will become more clearly apparent after a study o-f the following specification, when read in connection with the accompanying drawings, in which:

FIGURE l is a cross-sectional view through a fuse according to one embodiment of our invention;

FIGS. 2, 3, 4 and 5 are steps in the ferrulefuse tube assembly shown in FIG. l;

FIG. 6 illustrates the magnetic lforming step` in our method of making a fuse tube-ferrule assembly; and

FIG. 7 is a cross-section through a fuse according to a second embodiment of our invention.

Referring now to the drawings, in which like reference numerals are used throughout to designate like parts, for a more detailed understanding ofthe invention, and in particular to FIG. 1 thereof, a fuse tube 10 composed of insulating material has a central aperture 11 therethrough in which is disposed a fusible element 12 having copper strips 13 and 14 on the ends thereof which, in the assembling process, are bent around the ends of the fuse tube and along back over the side of the fuse tube and over the coatings on the outer wall of the fuse tube near the ends, these coatings lbeing shown at 15 and 16. As previously stated, the coatings 15 and 16 may be composed of silicon carbide grit on a brush coat of sodium silicate, or the coatings may be a single band or more of a pressure sensitive adhesive tape, depending upon the type of insulating material employed in the fuse tube. The fuse of FIG. 1 has ferrules 21 and 22 mounted on the ends thereof, and the central aperture 11 o-f fuse tube 10 is filled with suitable materials, for example, sand 23 at one end, a central portion 24 of calcium carbonate, with more sand 25 at the other end.

IParticular reference is made now to FIG. 2. A first step in assembling the fuse tube and ferrule may be to insert the fusible element 12 in the central aperture 11 of the fuse tube, to attach the two copper strips 13 and 14 to the ends of the fusible element, and extend the copper strips beyond the ends of the fuse tube. The coatings 15 and 16 may be applied at the ends of the fuse tube before or after the -fusible element is `inserted in the tube.

The next step may be that illustrated in FIG. 3, where the copper strip 13 is shown bent around the end of the fuse tube and bent along the outer wall of the `fuse tube over the aforementioned layer or coating 15. This is done at both ends of the fuse tube, although for simplicity of illustration only one end of the tube is shown.

The next step, FIG. 4, may be to Slightly bend the copper strip 13 so that it is more nearly extending in an axial direction along the central bore 11 of the fuse tube. This is done at both ends of the fuse tube. The next step may -be that illustrated in FIG. 5, where it is seen that one ferrule is slipped over the end of the fuse tube and the coating thereon.

One ferrule may be pushed -or slipped in place, the central aperture of the fuse tube lled with sand and calcium carbonate and the other ferrule pushed into place. One end of the fuse tube with the attached ferrule is then inserted in a coil 31 of a magneforming machine generally designated 32. The magneforming machine 32 is shown as having a control 33 for connecting the capacitors of the machine in such a manner as to produce a very high current pulse through the coil 31. The coil 31 is mechanically very rigid so that substantially no movement of the coil itself takes place as a result of the pulse of current and very large forces are created in the ferrule which crimp or compress the ferrule into very firm engagement with the fuse tube. The magneforming process has been described in detail elsewhere in the literature and need not be described in detail here. After one end of the fuse has the ferrule firmly attached, the ends of the fuse are reversed and the other ferrule, for example, ferrule 22 is inserted in the coil 31 and the process repeated.

The excess wire ends 27 and 28, FIGS. 2 to 5, may be trimmed as a final step in finishing the fuse.

As previously stated, the result of this method of making a fuse is an extremely strong fuse in which the ferrules are very securely attached, and pressure built up within the fuse as a result of inductive energy released when the circuit is broken does'not disrupt the fuse.

Particular reference is made now to FIG. 7, where another embodiment of our invention is shown. In FIG. 7 the fusible element 42 is a length of wire of suitable material. Wire 42 has copper strips 13 and 14 secured to the ends thereof. Otherwise the construction of the fuse of FIG. 7 is similar to that of FIG. l, except that the interior bore or passageway 11 of the fuse tube is filled with sand 39.

There has been provided, then, a fuse well suited to fulfill the aforedescribed objects of the invention, which `are to provide a new and improved fuse having a ferrulefuse tube assembly characterized by great mechanical strength. In addition, we have described a new and irnproved method of constructing a fuse, including the step of attaching the ferrule to the fuse tube by compressing the ferrule with magnetic force.

Whereas we have described our apparatus invention for illustrative purposes with respect to two embodiments thereof, it will be understood that changes may be made and equivalents substituted without departing from the spirit and scope of the invention.

It will be understood that the method of our invention may be employed to construct fuses having different congurations from those shown for illustrative purposes, and that our method is not limited to constructing yfuses of the types shown.

We claim as our invention:

1. The method of constructing afuse which comprises the steps of inserting a fusible element in a fuse tube,

attaching strips of conductive material to the ends of the fusible element, applying a coating of yieldable material to the outer surface of the fuse tube at both ends thereof, 4bending the conductive strips around the ends of the fuse tube, further bending the conductive strips adjacent the coatings, slipping a ferrule on one end of the fuse tube over the coating and conductive strip, filling the central aperture of the fuse tube with a filler material, slipping an additional ferrule on the other end of the fuse tube over the coating and conductive strip, and thereafter subjecting both the ferrules to magnetic induction thereby producing intense forces in the ferrules which bend the lferrules into very firm engagement with the adjacent surfaces of the fuse tube.

2. The method of constructing a fuse which comprises the steps of inserting conductive means including fusible means in series therein through a fuse tube having coatings of yieldable material on the outside wall thereof near the ends thereof, bending the ends of the conductive means around the adjacent ends of the fuse tube and into the coatings respectively, adding a filler material to the central aperture of the fuse tube, slipping ferrules on the ends of the fuse tube over the ends of the conductive means and over the coatings, the ferrules making electrical connection with the conductive means, and thereafter subjecting the ferrules to magnetic induction thereby exerting strong forces on the ferrules which cause them to bend and grip very strongly the ends of the fuse tube and insure permanent electrical connection with the adjacent portions of the conductive means.

3. The method of constructing a fuse which comprises the steps of coating the outer surface of a fuse tube near the endsthereof with a resilient coating material, attaching strips of conductive material to the ends of a fusible element, inserting the fusible element with the strips attached through the fuse tube, bending the ends of the conductive strips around the ends of the fuse tube and into the coatings, slipping a ferrule on one end of the fuse tube over the coating and conductive strip, lling the central aperture of the fuse tube with a filler material, slipping an additional ferrule on the other end of the fuse tube over the coating and conductive strip, and thereafter subjecting the ferrules sequentially to magnetic induction thereby producing intense forces in the ferrules which bend the ferrules into very firm engagement with the adjacent surfaces of the fuse tube.

References Cited UNITED STATES PATENTS 1,077,369 11/1913 Roberts 200-120 1,140,953 5/1915 Cole 200-120 2,157,907 5/1939 Lohausen 20D-131 X 2,333,354 11/1943 Andersen et al 200-121 2,691,083 10/1954 Hitchcock 200-132 2,847,537 8/1958 Kozacka 200 120 X 3,094,600 6/ 1963 Kozacka ZOO-132 3,196,649 7/1965 Furth 317-158 X FOREIGN PATENTS 479,211 2/ 1938 Great Britain.

BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

1. THE METHOD OF CONSTRUCTING A FUSE WHICH COMPRISES THE STEPS OF INSERTING A FUSIBLE ELEMENT IN A FUSE TUBE, ATTACHING STRIPS OF CONDUCTIVE MATERIAL TO THE ENDS OF THE FUSIBLE ELEMENT, APPLYING A COATING OF YIELDABLE MATERIAL TO THE OUTER SURFACE OF THE FUSE TUBE AT BOTH ENDS THEREOF, BENDING THE CONDUCTIVE STRIPS AROUND THE ENDS OF THE FUSE TUBE, FURTHER BENDING THE CONDUCTIVE STRIPS ADJACENT THE COATINGS, SLIPPING A FERRULE ON ONE END OF THE FUSE TUBE OVER THE COATING AND CONDUCTIVE STRIP, FILLING THE CENTRAL APERTURE OF THE FUSE TUBE WITH A FILLER MATERIAL, SLIPPING AN ADDITIONAL FERRULE ON THE OTHER END OF THE FUSE TUBE OVER THE COATING AND CONDUCTIVE STRIP, AND THEREAFTER SUBJECTING BOTH THE FERRULES TO MAGNETIC INDUCTION THEREBY PRODUCING INTENSE FORCES IN THE FERRULES WHICH BEND THE FERRULES INTO VERY FIRM ENGAGEMENT WITH THE ADJACENT SURFACES OF THE FUSE TUBE. 